The present invention relates to a flexible electrically conductive sheet for being interposed between two objects to pass a weak current such as an electrostatic current for keeping the objects at the same electric potential.
Synthetic fibers and plastic films produce static electricity when they are rubbed against each other or something else under a dry condition. The polarity of the generated static electricity may be positive or negative dependent on the type of the synthetic fibers and plastic films. The voltage of the generated static electricity is proportional to the electric insulation capability of the synthetic fibers and plastic films, and may range from several thousands to several tens of thousand volts.
In the textile industry, the static electricity causes synthetic fibers to be repelled from each other while the fibers are being spun or woven, or causes synthetic fibers to be attracted to machinery, resulting in an operation failure. When manufacturing plastic films, static electricity developed in plastic films is discharged to cause operation problems. Moreover, electronic devices comprising microcomputers or the like, such as office automation devices, placed on an insulative floor made up of wood in a dry room are electrostatically charged during usage, and charged static electricity causes the electronic devices to malfunction or erroneous data to be input or output.
Various efforts have been made to prevent troubles due to electrostatic charging. For example, an atomizer is disposed in a spinning or weaving factory or a plastic film factory to keep the humidity in the factory at 75% or higher at all times. While fibers or plastic films are much less electrostatically charged by the controlled humidity in the factory, it is impossible to completely remove electrostatic charging.
Another proposal is a corona-discharge electrostatic charge remover in which a remover electrode and an installed electrode are provided as means for removing static electricity. A corona discharge is generated between the electrodes to produce ions which are applied to a charged body to neutralize the static electricity, and unnecessary ions are attracted to the installed electrode. However, the corona-discharge electrostatic charge remover is large and complex, and hence highly costly.
According to a further attempt, a rubber sheet with an electrically conductive filler such as carbon black being mixed therein is attached to the circumferential surface of a metallic roller. The energy of static electricity generated can be consumed by the internal resistance of the rubber sheet. As an alternative, electrostaticaly charged objects are brought into contact with a belt made of such electrically conductive rubber to discharge the electrostatic energy. If the rubber sheet is to be of a low resistance, a large amount of filler must be mixed, thus making the rubber sheet brittle and less durable. If the amount of mixed filler is reduced to render the rubber sheet less brittle, no sufficient resistance is obtained, and generated static electricity cannot fully be removed.